Supporting wheel

ABSTRACT

A non-pneumatic supporting wheel includes a central part and a wheel-rim which is supported by the central part. The wheel-rim has an outer wheel-rim part which is intended to roll against an underlying surface, and an inner wheel-rim part which is located radially inwards of the outer wheel-rim part. At least the inner of the two wheel-rim parts is constructed from a plurality of curved, elongated elements which consist of a resilient material and which are spaced in the circumferential direction of the wheel. When seen in a section taken diametrically through the wheel, each of these elements presents parts which are curved in opposite directions. For the purpose of taking-up forces which act substantially radially between the wheel center and the region of the wheel in contact with the underlying surface when the wheel is subjected to load, the elements are elastically yielding in the radial direction of the wheel during increased bending of the elements. The circumferentially spaced and bendable elements are constructed so that both the sum of the bending of each small longitudinal section of the elements when the elements are subjected to load in the radial direction of the wheel and the sum of the product of the bending of each small section and the distance of this section from the underlying surface when the wheel is subjected to normal load is at least essentially zero.

This invention relates to a non-pneumatic supporting wheel of the kindcomprising a central part and a wheel-rim, which is carried by saidcentral part and which has an outer wheel-rim part, which is intended toroll on an underlying surface, and an inner wheel-rim part, locatedradially inwards of said outer wheel-rim part, wherein at least theinner of the two wheel-rim parts is constructed from a plurality ofcurved elongated elements which consist of a resilient material andwhich are mutually separated in the circumferential direction of thewheel, and wherein each of said elongated elements, when seen in asection taken diametrically through the wheel, present parts which arecurved in opposite directions, and which elements, for the purpose oftaking-up forces which, when the wheel is subjected to load, actsubstantially radially between center of the wheel and the regionthereof in contact with the underlying surface, are elastically yieldingin the radial direction of said wheel during increased bending of saidelements.

In the case of known non-pneumatic support wheels, see for instance U.S.patent application No. 2,436,844 and 4,350,196 and WO 87/05268, theouter wheel-rim part tends to move to one side upon contact with theunderlying surface. This can result in drawbacks in the form ofincreased wear on the material which comes into contact with theunderlying surface, increased stresses on wheel bearings, impaired roadholding of a vehicle which is fitted with such non-pneumatic supportingwheels, and, above all, higher internal losses as a result ofpropagation of the lateral movements of that wheel-rim region in contactwith the underlying surface to adjacent regions of the wheel andresultant deformation of said regions.

The object of the present invention is to provide a novel and usefulsupporting wheel in which the aforesaid drawbacks are at leastsubstantially avoided.

To this end, it is proposed in accordance with the invention that in thecase of a supporting wheel of the kind described in the introduction,the bendable elements which are mutually spaced in the circumferentialdirection of the wheel are so constructed that both the sum of thebending of each small longitudinal section of the elements when saidelements are subjected to load in the radial direction of the wheel, andthe sum of the product of the bending of each such small section and thedistance of this section from the underlying surface when the wheel issubjected to normal load is at least substantially zero. As a result ofthis arrangement, the supporting wheel will be deformed elasticallysubstantially only in the radial direction when in contact with theunderlying surface.

The aforedescribed, inventive construction of the elongated resilientelements can be achieved in many different ways in practice. However, apreferred embodiment of the invention is characterized in that theelements or the parts thereof which form the inner wheel-rim part ofsaid wheel have, when seen in a section taken diametrically through thewheel, essentially the form or a recumbent S with the end of a radiallyoutward convex part being located on one side of the wheel and connectedto the central part of said wheel, and the end of a radially inwardconvex part being connected to the outer wheel-rim part on the oppositeside of said wheel.

When the outer wheel-rim part has the form of a circumferentiallyextending web, it is particularly advantageous to provide the web withradially through-passing holes. These holes, which extend through theouter wheel-rim part, have surprisingly been found to reduce the levelof noise that is generated when the supporting wheel rolls against theunderlying surface. It has been possible to achieve noise reductions ashigh as 10 dBA, with a suitable choice of hole size and shape.

The invention will now be described in more detail with reference to theaccompanying drawings.

FIG. 1 is a schematic axial-section partial view of an inventivenon-pneumatic supporting wheel, with the wheel shown in a load-freestate.

FIGS. 2 and 3 are simplified axial-section partial views of anon-pneumatic supporting wheel similar to the wheel of FIG. 1 andillustrate the principles of the invention, said wheel being shown in aloaded state in said Figures.

In the drawings, the reference numeral 10 identifies generally a centralpart of a non-pneumatic supporting wheel, for instance the wheel of anautomotive vehicle, whose geometric axis is referenced 11. The centralpart 10 comprises two discs 12, which may be provided with holes (notshown) by means of which the wheel can be fitted, for instance, to awheel hub, and a disc 13 which is held between the discs 12. The wheelalso includes a wheel-rim which is carried by the part 10 and which hasan outer, circumferentially extending wheel-rim part 14, having an outersurface tread layer 15 made, for instance, of rubber or plastic materialand intended for contact with the underlying surface, or rollingsurface, and an inner wheel-rim part which is comprised of a pluralityof elongated, curved elements 16. These elements 16, the inner ends ofwhich connect with the disc 13, are mutually spaced in thecircumferential direction of the wheel and, when seen in a section takendiametrically through the wheel, present, in the manner shown,oppositely curved parts 17, 18, which are located on respective sides ofan imaginary plane extending through the loading center CL (FIGS. 2 and3), this plane extending through the wheel at right angles to the axis11 at a location. In a normal case, this location lies midway betweenthe opposite sides of the wheel and the opposite sides of the outersurface tread layer 15 in contact with the underlying rolling surfacerespectively. When the wheel is subjected to load, forces actsubstantially radially between the center 11 of the wheel and thatregion of the outer layer which is in contact with the underlyingsurface. An essential part of these forces is taken-up by the elements16 as bending of the curved parts 17, 18 increases. The resilientelements 16 have been constructed in a manner to fulfill the followingtwo conditions simultaneously, by appropriate selection of the materialfrom which said elements are made coupled with suitable selection oftheir dimensions and shapes, these conditions being:

a) that the sum of the extent to which each small longitudinal sectionΔ1_(k), Δ1_(m), Δ1_(j), Δ1_(n) of the elements 16 bends when theelements are subjected to load (within the intended wheel loading range)is zero or at least substantially zero; and

b) that the sum of the product of the extent to which each such smallsection Δ1_(j), Δ1_(n) bends and the distance h_(j), h_(n) of thissection from the underlying surface is zero or at least substantiallyzero.

The condition a) is illustrated (greatly exaggerated for the sake ofclarity) with the loaded wheel shown in FIG. 2, where a force or a loadacting-on the outer surface tread layer 15 in the region of its contactwith the underlying surface is assumed to be evenly distributed over thewhole width of the contact region and has a force resultant which actsin the load center CL perpendicularly to the underlying surface. Theload exerted on the wheel causes each small piece or section Δ1_(k),Δ1_(m) of the curved elements 16 concerned to bend from a load-freestate, shown in broken lines, through an additional angle of curvaturev_(k), v_(m) to the loaded state illustrated in full lines. Thisadditional angular value is, of course, contingent on the size of theload. This further bending v_(k) of the elements 16 on one side of theload center CL will therewith cause the outer wheel-rim part to beobliquely positioned in one direction as this wheel-rim part movesinwardly through a distance which, in the CL-plane, has the lengthr_(k), whereas the further bending v_(m) of the element 16 on the otherside of the load center CL will cause the outer wheel-rim part to bepositioned obliquely rearwards in the other direction, as this partmoves inwards through a distance which, in the CL-plane, has the lengthr_(m). The sections Δ1_(k) and Δ1_(m) are representative of other smalllength sections of the elements 16 on one or the other side respectivelyof the load center CL. The result of the directive or condition a) isthus that the outer wheel-rim part will retain its parallelity with theunderlying surface in the region of its contact with said surface, withthe load uniformly distributed over the whole width of the wheel duringradial movement. The condition a), however, does not exclude lateralmovement of the region of the outer wheel-rim part in contact with theunderlying surface relative to adjacent regions of this wheel-rim part,and consequently the condition b) is prescribed in order to rectifythis. The condition b) is illustrated (greatly exaggerated for the sakeof clarity) with a loaded wheel in FIG. 3, where a force or load actingon the outer surface tread layer 15 in the region of its contact withthe underlying surface is assumed to be uniformly distributed over thewidth of the wheel and to have a force resultant which acts in loadcenter CL perpendicularly to the underlying surface. The load causeseach small piece or section Δ1_(j), Δ1_(n) of the curved element 16concerned to bend through a further angle v_(j), v_(n), from anon-loaded state, shown in broken lines, to a loaded state shown in fulllines. The size of this further angle is, of course, contingent on thesize of the load. This further bending v_(j) of the section Δ1_(j) ofthe element 16 on one side of the load center CL will therewith attemptto move the outer wheel-rim part laterally in one direction through adistance a_(j) whose length is contingent on the product of the furtherbending v_(j) and the distance h.sub. j of the section Δ1_(j) from theunderlying surface, whereas the further bending v_(n) of the sectionΔ1_(n) of the element 16 on the opposite side of the load center CL willstrive to move the outer wheel-rim part laterally, back in the oppositedirection through a distance a_(n), whose length is contingent on theproduct of the further bending v_(n) of this section Δ1_(n) and thedistance h_(n) of said section from the underlying surface. The sectionsΔ1_(j) and Δ1_(n) are representative of remaining small length-sectionsof the element 16 located on one and the other side of the load centerCL respectively. Thus, the result of condition b) is that the outerwheel-rim part will not be moved laterally in the region of its contactwith the underlying surface, and consequently the result of condition b)in combination with the result of condition a) will result insubstantially optimal function of the supporting wheel.

In FIGS. 1-3, the elements 16, when seen in a section takendiametrically through the wheel, have substantially the form of arecumbent S, with the end 21 of a radially outward convex part 17located on one side of the supporting wheel and adjoining the centerpart of said wheel, more specifically the adjoining radially outerregion of the disc 13, and with the end 22 of a radially inward convexpart 18 adjoining the outer wheel-rim part 14, 15 on the opposite sideof the wheel. In this way, a relatively small space is required radiallyfor the resilient elements 16. It is also possible, however, to give theresilient elements 16 essentially the form of an upstanding S, withconvex, resilient parts located on a first and a second siderespectively of said wheel, substantially on opposite sides of theload-center plane CL and at different radial distances from the tread15, although respect must be paid to the fact that when the resilientelements bend, those parts of the elements 16 which are located far fromthe underlying surface will cause greater lateral movement of thatregion of the outer wheel-rim part in contact with the underlyingsurface than those parts of the elements 16 which are located close tosaid surface. For example, those parts which are distal from theunderlying surface are made more rigid than those parts which arelocated close to said surface.

The outer, circumferentially extending wheel-rim part 14, and the outersurface tread 15 may advantageously be constructed of radially outerend-parts 19 or continuations of the resilient, elongated, curvedelements 16 mutually spaced in the circumferential direction of thewheel, said end parts extending substantially horizontally from theregion 22 on one side of the wheel towards and past the CL-plane, to theother side of said wheel. These end parts or continuations 19 may beembedded in the tread material, such as rubber or plastic material,either individually or, as shown, commonly. In the former case, thetread will thus also consist of peripherally separated regions, while inthe latter case the tread will extend continuously around the wheel. Itis also possible to construct the outer wheel-rim part as asubstantially cylindrical ring of resilient material which is clad withtread material and to which the regions 22 of the elements 16 connect.It is also possible to construct the wheel more or less completely fromcomposite material.

At least when the outer wheel-rim part 14, and the layer 15 are in theform of a circumferentially extending, continuous web, it is suitable toform radially through-passing holes 20 in said web, in the mannerillustrated, in order to reduce the level of noise that is generatedwhen the wheel runs on the underlying surface. More specifically, theouter wheel-rim part 14, and the layer 15, in accordance with FIG. 1,are provided with rows of through-passing holes 20 which extendcompletely through both the tread material 15 and the tread-supportingstructure 14, so as obtain "ventilation" between the outer surface ofthe outer wheel-rim part and the radially inwardly facing inner surface23 of said wheel-rim part. The holes 20 are arranged in pattern cavities24 in that side of the web or tread intended for contact with theunderlying surface. The size, shape and number of the holes 20 used toreduce sound emission can vary from case to case and the holes may alsohave a cross-sectional area which varies along their respective lengths.

The combined area of the holes 20 should, however, lie between 2 and 50%of the total area of the side of the web or tread intended for contactwith the underlying surface. The holes may be from 100 to 1,000 innumber and may have a combined hole-area of at least 3%, suitably atleast 5% and preferably at least 7% of the area of said web or treadside, and at most 30% and suitably at most 25% of the area of said webside.

An advantage is afforded when at least some of the holes 20 are arrangedin the bottom of pattern cavities 24 in the web side intended forcontact with the underlying surface, in the manner shown, and holes ofdifferent sizes and/or with irregular positioning in the outer wheel-rimpart can be used, in order to avoid undesirable resonance phenomena,among other things. The holes may have any desired shape and at leastsome of the holes may have the form of slots or slits, wherein the holesor the slits may have a diameter or a smallest cross-dimension of 1-20mm. At least some of the holes on the side 23 of the outer wheel-rimpart 14 facing towards the wheel center may open into cavities having ashape and size selected for the absorption of noise within a determinedfrequency range. Noise reductions as high as 10 dBA have been obtainedin practice with hole arrangements of the aforedescribed kind.

The invention is not restricted to the embodiments described above withreference to the drawings, but can be realized in any desired mannerwithin the scope of the inventive concept defined in the followingclaims.

I claim:
 1. A non-pneumatic supporting wheel comprising:a central; and awheel-rim, having an inner wheel-rim part and an outer wheel-rim part,carried by said central part, said outer wheel-rim part rolling on anunderlying surface and said inner wheel-rim part located radiallyinwards of the outer wheel-rim part; said inner wheel-rim part includinga plurality of curved, elongated, bendable elements which consist of aresilient material and are separated from one another in acircumferential direction of the wheel; each of said curved, elongated,bendable elements having the shape of a recumbent S so that (a) one endof a radially outwardly convex portion of each of said curved,elongated, bendable elements is located on one side of the wheel and isconnected with said central part of the wheel and (b) a remote end of aradially inwardly convex portion of each of said curved, elongated,bendable elements is located on an opposite side of the wheel and isconnected with said outer wheel-rim part of said wheel-rim; wherein saidcurved, elongated, bendable elements, in order to take up forces which,when the wheel is subjected to load, act substantially radially betweensaid central part of the wheel and said outer wheel-rim part, areelastically resilient in a radial direction of said wheel duringincreased bending of said curved, elongated, bendable elements, andwherein said curved, elongated, bendable elements are constructed sothat both a sum of each longitudinal bending increment (Δ1_(k), Δ1_(m),Δ1_(j), Δ1_(n)) of the curved, elongated, bendable elements and a sum ofa product of each longitudinal bending increment (Δ1_(j), Δ1_(n)) and adistance (h_(j), h_(n)) between each longitudinal bending increment,respectively, and the underlying surface is zero when the wheel issubjected to normal load in the radial direction.
 2. A supporting wheelaccording to claim 1, wherein the curved, elongated, bendable elementsall include radially outer end parts so that the outer wheel-rim part isformed at least partially by said radially outer end parts of thecurved, elongated, bendable elements.
 3. A supporting wheel according toclaim 2, wherein the radially outer end parts of the curved, elongated,bendable elements are embedded in at least one of a rubber and a plasticmaterial intended for contact with the underlying surface.
 4. Asupporting wheel according to claim 1, wherein the outer wheel-rim partis a circumferentially extending web provided with between 100 and 1000radially through-passing holes.
 5. A supporting wheel according to claim4, wherein a combined area of the through-passing holes is between 5 and30% of a total area of the material intended for contact with theunderlying surface.
 6. A supporting wheel according to claim 4, whereinthe outer wheel-rim part includes pattern cavities provided therein andat least some of the through-passing holes are arranged in bottoms ofsaid pattern cavities.
 7. A supporting wheel according to claim 4,wherein the through-passing holes have different sizes.
 8. A supportingwheel according to claim 7, wherein the through-passing holes areirregularly positioned.
 9. A supporting wheel according to claim 4,wherein at least some of the through-passing holes open out towards thecentral part of said wheel into cavities having shapes and sizes whichare selected to promote absorption of noise within a determinedfrequency range.
 10. A supporting wheel according to claim 4, whereinthe through-passing holes have a smallest cross-dimension of 1-20 mm andat least some of the through-passing holes are formed as slits.
 11. Asupporting wheel according to claim 4, wherein the through-passing holesare irregularly positioned.